Extraction of phenols



Patented Jan. 30, 1934 STATES PATENT OFFICE EXTRACTION OF PHENOLS WalesNo Drawing. Application March 5, 1931, Serial No. 520,479, and inAustralia April 4, 1930 3 Claims.

In the known process of extracting phenols, phenol homologues, and otherhydroxy aromatic compounds from oils, crude phenates, cresylates, andlike compounds obtained by washing the oil with caustic soda or otheralkali hydroxide, are decomposed with acid and settled out and the crudetar acids thus liberated are separated by distillation. In thedistillation step, neutral oils, pyridine, naphthalene, and certainother substances come overwith the acids, and the products are thusrendered impure. The impurities unfit the acids for many uses, as forinstance in the manufacture of synthetic resins and fine antiseptic s.

The impurities are frequently found to amount to as much as in a crudeacid prepared as above. In the known method of purification, the crudephenate or cresylate or like compound is heated with steam andsimultaneously blown with air, which process removes naphthalene andneutral oil, but must be continued for a considerable period in the mostfavourable circumstances to obtain the desired result, and in some casesis carried on for as long as forty-eight hours, and is attended by aconsiderable loss of tar acids as hydrolysis is considerable at thetemperature at which blowing is conducted.

Phenates, cresylates, and like compounds derived from horizontal retortand coke oven tars contain impurities which have a relatively high vaporpressure. The known process is more or less effective for the treatmentof those products; but the phenates, cresylates, and like compoundsobtained from low temperature tar oils, cracked mineral oils, or shaleoil contain impurities which have a relatively low vapor pressure, andfor the treatment of these oils it has been found necessary to prolongthe process of purification by steam or air blowing, with theconsequence that loss of tar acid product is substantially increased;the degree of refinement attained is also unsatisfactory.

The present invention consists in distilling the phenates, cresylates,or like compounds in aqueous solution containing the impurities, un-

der high vacuum, before the tar acids are liberated from it by treatmentwith mineral acid, carbonic acid, or other reagent. The neutral oils andother impurities which will distil at subsequent stages of refining arethus taken ofi. The tar acids are held in combination with the alkali,and as they are not volatile when in such combination, they remain inthe still with a proportion of heavy and gummy impurities which do notpass over; these heavy and gummy impurities, however, cause nodifliculty in the later steps in the process.

The known process is then again followed, and the still liquor fromwhich the impurities have been removed in the distillation step aretreated with sulphuric acid or carbon dioxide, following known practice,to liberate the tar acids. The mixed acid product thus obtained isfractionated under appropriate temperature and pressure conditions toobtain the particular phenols or other tar acids required. Thedistillate acids may be treated by air blowing or with a metallic oxideand subjected to final redistillation to obtain them in a condition ofgreat purity.

The removal of the impurities by distillation prior to the decomposingof the alkali phenolic or similar compounds is efiected under highvacuum. It is desirable that the vacuum should be as high aspracticable; the results are less satisfactory as the vacuum falls.

In practice the process is operated as follows:

Sodium cresylate solution of specific gravity about 1.075 obtained fromwashing tar oil is run to settling tanks where any oil that settles outon standing for twelve hours is skimmed off.

The cresylate solution is then pumped to a vacuum pan; a single effectpan such as used for concentration of weak caustic soda liquor issuitable for this operation. The charge is boiled vigorously under avacuum of 27-28" vacuum; the bulk of the oil and bases come away in thefirst five minutes. However, to obtain acid which gives a completelymiscible solution in caustic soda it is necessary to prolong theprocess; when so prolonged the process is generally completed inforty-five minutes.

The completeness of the operation can be determined by decomposing asmall sample of the cresylate with sulphuric acid, distilling theseparated cresylic acid, and re-dissolving in 10% caustic soda solution.

The refined sodium cresylate can then be decomposed by known process anddistilled.

What I claim as my invention and desire to secure by Letters Patent is:-

1. In the recovery of phenols from tar oils by extraction with asolution of a hydroxide of an alkali metal, the step of removing neutraloils and other alkali insoluble bodies from the solution which stepcomprises distilling the solution of phenols in the hydroxide of analkali metal at a pressure substantially below atmospheric pressure.

2. In the recovery of phenols from tar oils by 3. The herein describedmethod of removing neutral oils from a caustic soda phenolate solution,comprising distilling the solution at a pressure substantially belowatmospheric pressure.

JVOHN GRIFFITH PEAKE.

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